26 research outputs found

    Tight binding description of the STM image of molecular chains

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    A tight binding model for scanning tunneling microscopy images of a molecule adsorbed on a metal surface is described. The model is similar in spirit to that used to analyze conduction along molecular wires connecting two metal leads and makes it possible to relate these two measurements and the information that may be gleaned from the corresponding results. In particular, the dependence of molecular conduction properties along and across a molecular chain on the chain length, intersite electronic coupling strength and on thermal and disorder effects are discussed and contrasted. It is noted that structural or chemical defects that may affect drastically the conduction along a molecular chain have a relatively modest influence on conduction across the molecular wire in the transversal direction.Comment: 22 pages, 9 figures, Israel J Chemistry, in pres

    12 DNA Conduction:  the Issue of Static Disorder,  Dynamic Fluctuations and Environmental Effects

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    12.2.1 Single-molecule transport experiments 438 12.2.2 Transport experiments on bundles and networks 44

    in Solution Chemistry Experiments.................... 188

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    Abstract Charge migration along DNA molecules has attracted scientific interest for over half a century. Reports on possible high rates of charge transfer between donor and acceptor through the DNA, obtained in the last decade from solution chemistry experiments on large numbers of molecules, triggered a series of direct electrical transport measurements through DNA single molecules, bundles, and networks. These measurements are reviewed and presented here. From these experiments we conclude that electrical transport is feasible in short DNA molecules, in bundles and networks, but blocked in long single molecules that are attached to surfaces. The experimental background is complemented by an account of the theoretical/computational schemes that are applied to study the electronic and transport properties of DNA-based nanowires. Examples of selected applications are given, to show the capabilities and limits of current theoretical approaches to accurately describe the wires, interpret the transport measurements, and predict suitable strategies to enhance th

    Direct monitoring of the stepwise condensation of kinetoplast DNA networks

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    Abstract Condensation and remodeling of nuclear genomes play an essential role in the regulation of gene expression and replication. Yet, our understanding of these processes and their regulatory role in other DNA-containing organelles, has been limited. This study focuses on the packaging of kinetoplast DNA (kDNA), the mitochondrial genome of kinetoplastids. Severe tropical diseases, affecting large human populations and livestock, are caused by pathogenic species of this group of protists. kDNA consists of several thousand DNA minicircles and several dozen DNA maxicircles that are linked topologically into a remarkable DNA network, which is condensed into a mitochondrial nucleoid. In vitro analyses implicated the replication protein UMSBP in the decondensation of kDNA, which enables the initiation of kDNA replication. Here, we monitored the condensation of kDNA, using fluorescence and atomic force microscopy. Analysis of condensation intermediates revealed that kDNA condensation proceeds via sequential hierarchical steps, where multiple interconnected local condensation foci are generated and further assemble into higher order condensation centers, leading to complete condensation of the network. This process is also affected by the maxicircles component of kDNA. The structure of condensing kDNA intermediates sheds light on the structural organization of the condensed kDNA network within the mitochondrial nucleoid

    © 2007 Nature Publishing Group ARTICLES

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    Electronic structure of single DNA molecules resolved by transverse scanning tunnelling spectroscop

    The puzzle of contrast inversion in DNA STM imaging (issue cover)

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    DNA has been at the center of an imaging effort since the invention of the scanning tunneling microscope (STM). In some of the STM imaging reports the molecules appeared with negative contrast, i.e., ``submerged'' under the metal background and darker. We demonstrate the phenomenon of contrast inversion in DNA STM imaging by controlled and spontaneous contrast inversions and by the dependence of the DNA apparent height with respect to the surface on the imaging bias voltage. Using these characterizations, we formulate a model explaining the above phenomenon by resonant tunneling through virtual states in the vacuum between the STM tip and the DNA molecule

    Tunable Length and Optical Properties of CsPbX<sub>3</sub> (X = Cl, Br, I) Nanowires with a Few Unit Cells

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    Perovskite nanostructures, both hybrid organo–metal and fully inorganic perovskites, have gained a lot of interest in the past few years for their intriguing optical properties in the visible region. We report on inorganic cesium lead bromide (CsPbBr<sub>3</sub>) nanowires (NWs) having quantum confined dimensions corresponding to 5 unit cells. The addition of various hydrohalic acids (HX, X = Cl, Br, I) was found to highly affect the NW length, composition, and optical properties. Hydrochloric (HCl) and hydroiodic (HI) acids mixed in the reaction solution influence the crystal structure and optical properties and shorten the NWs, while the hydrobromic acid (HBr) addition results solely in shorter NWs, without any structural change. The addition of HX increases the acidity of the reaction solution, resulting in protonation of the oleylamine ligands from oleylamine into oleyl-ammonium cations that behave similarly to Cs<sup>+</sup> during crystallization. Therefore, the positions of the Cs<sup>+</sup> at the growing surface of the NWs are taken by the oleyl-ammonium cations, thus blocking further growth in the favored direction. The emission of the NWs is tunable between ∼423–505 nm and possesses a potential in the optoelectronic field. Moreover, electrical conductivity measurements of the NWs are discussed to give a new point of view regarding the conductivity of perovskite nanostructures
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